1. Field of Invention
This invention relates to wireless communications systems. Specifically, the present invention relates to systems and methods for facilitating wireless phone service acquisition via the use of a preferred roaming list.
2. Description of the Related Art
Wireless phones and associated wireless telecommunications systems are used in a variety of demanding applications including search and rescue and business applications. Such applications demand communications systems that provide effective service to a wireless phone as it travels or roams between geographic regions.
Wireless telecommunications systems are characterized by a plurality of mobile stations (e.g. wireless phones, mobile phones, or cellular phones) in communication with one or more base stations. A signal transmitted by a mobile station is received by a base station and often relayed to a mobile switching center (MSC). The MSC in turn routes the signal to another base station, a public switched telephone network (PSTN) or to another mobile station. Similarly, a signal may be transmitted from the public switched telephone network to a mobile station via a base station and a mobile switching center.
A base station routes calls between mobile stations and a telecommunications network via a mobile switching center. Each base station governs a limited geographic region called a cell. Typically, the coverage area of a wireless telecommunications system is divided into several cells. Different communications resources such as frequencies are often allocated to each cell to maximize communications system resources. When a mobile station moves from a first cell to a second cell, a handoff is performed to assign new system resources associated with the second cell to the mobile station.
Often a particular geographic area in which wireless service is available has several cells or coverage areas. The cells may overlap and may be associated with different types of telecommunications systems such as cellular code division multiple access (CDMA) systems, cellular analog systems, personal communication system (PCS) CDMA systems, or advanced mobile phone system (AMPS) systems. For example, currently Canada has an AMPS coverage area that overlaps several different CDMA coverage areas. Each CDMA coverage area is associated with a different province.
Users often travel within and between different system coverage areas. Each system coverage area comprises one or more cells and may define a particular geographic region. A base station is often called a system. Each base station governing a particular geographic region broadcasts a system identification number (SID). The SID is detectable by the mobile station.
Upon initial power-up, a mobile station executes software to determine currently available wireless services and to acquire the most preferable available service. Mobile station manufacturers distribute mobile stations to wireless carriers such as Sprint(copyright) or Airtouch Cellular(copyright). Each wireless carrier typically has an option to program information into the mobile station specifying the frequencies and the relative priorities of different types of services detected. For example, once the mobile station detects a SID transmitted by a base station, the mobile station may compare the SID with pre-existing information in a mobile station memory. If for example, a wireless carrier such as Airtouch provides a mobile station to a user, the programmed information may specify Airtouch base stations as representing desirable Systems and may specify certain other types of systems as non-acceptable. The wireless carriers may define particular geographic regions that comprise one or more system coverage areas, i.e., cells. The wireless carriers may establish via software, which of the coverage areas in the particular geographic region are preferable for mobile station acquisition. However, once a mobile station acquires a particular system that may extend beyond the particular geographic region, the mobile station is oblivious as to when it exits the geographic region and enters an area in which more desirable service may exist. Similarly, once a mobile station obtains service from a base station, i.e., a system, the mobile station maintains that service while inside the coverage area of that base station with that base station, even if more desirable systems exist. This may result in inefficient use of network resources and may result in inferior mobile phone performance when roaming.
Hence, a need exists in the art for an efficient system and method for searching for the availability of different and possibly more desirable wireless services and th,at accounts for movement of the mobile station through different geographic coverage areas. There is a further need for a system and method for facilitating the acquisition of the optimal service given that one or more wireless services is currently available.
The need in the art is addressed by the system for facilitating the acquisition of a most desirable wireless service for a wireless phone of the present invention. In the illustrative embodiment, the inventive system is adapted for use with a wireless phone having a computer. The system includes a scanning mechanism for periodically scanning for a signal indicative of a wireless service having a coverage area that overlaps one or more coverage areas of other wireless services. The system further includes a service acquisition mechanism for acquiring the wireless service or one of the other wireless services across different geographic regions based on predetermined selection criteria and said signal.
More specifically, the present invention includes a wireless phone that includes a first mechanism for determining if a detected service, i.e., communications system, is associated with multiple coverage areas that overlap one another. A second mechanism compares the different systems in these coverage areas to the detected system and selects a preferred system based on the comparison.
In a specific embodiment, the wireless phone includes a computer that runs software for implementing the first, second, and third mechanisms. The first mechanism includes a mechanism for providing a data structure that contains identification information for each system associated with multiple geographic regions. The identification information includes a list of system
In the illustrative embodiment, the second mechanism includes a mechanism for checking if a preferred/negative indicator in the preferred roaming list in the wireless phone is set to preferred or negative for each of the different systems and/or the detected system, which are systems under comparison. The second mechanism also assigns a lowest priority to each of the systems under comparison that are associated with a negative indicator. The second mechanism also includes a mechanism for determining if the wireless phone has a forced mode or a preferred mode and for assigning a higher priority to each of the systems under comparison that correspond to the forced mode or the preferred mode. If the wireless phone is not set to a forced or preferred mode, an additional mechanism determines if the systems under comparison are code division multiple access systems or advanced mobile phone systems or a combination thereof and selects the system of the type assigned a higher priority in the data structure, which is a preferred roaming list. Finally, the invention includes a mechanism for analyzing a roaming indicator for the systems under comparison and subsequently assigning relative priorities to systems in accordance with roaming indicator status specifications detailed in the TSB58 standard.
The novel design of the present invention is facilitated by unique methods of the present invention that allow a mobile phone to detect newly available systems (known as candidate systems or target systems) and analyze the systems to determine if the mobile phone should switch to one of the newly available systems. Previously, if the coverage area of an initial wireless system overlapped the coverage areas of other perhaps more desirable systems, the mobile phone could not detect and switch to a more desirable system once service was acquired from the initial system.